The inventive concepts disclosed herein relate generally to the field of head up displays (HUDs) including but not limited to HUDs used in aircraft.
A HUD may be used by an operator of an aircraft or other equipment to allow the operator to have a view of an environment with superimposed information, such as symbols and images captured by sensors. Worn HUDs, including but not limited to head worn displays (HWDs), such as, helmet mounted displays (HMDs), are used in aircraft applications (e.g., both in in-flight applications and simulator applications), surface-based transportation applications, medical applications, robotic applications, entertainment applications, and other applications. Head worn displays include monocular type displays having a single display area (viewable by one or two eyes) and binocular type displays having separate left and right eye display areas. With a binocular type display, the left eye sees a left eye image display while the right eye sees a right eye image display.
Worn display systems also generally include a tracking system for tracking the position of the head or eyes of the user. Head tracking can be achieved through various techniques, most often in the form of magnetic tracking, ultrasonic tracking, inertial tracking, optical tracking and hybrid optical-inertial tracking. Optical tracking can either be achieved through outside-in sensing (where a system of cameras is mounted external to the object being tracked with active/unique fiducials mounted on the object of interest), or inside-out sensing (where a camera is mounted on the object of interest and tracks active/unique fiducials of the external scene). Eye tracking can be achieved using sensors configured to sense pupil position.
The tracking system provides information to a HUD computer so the HUD computer can cause the displayed symbology to appear conformal to the environment (e.g., the real world), even though the reference frame of the projection system is the pilot's head. Such tracking systems are often complex, costly and add latency to the worn display system and require some recognizable and measurable reference from which to infer the position of the pilot's head or eyes.